It is common for machinery and various powered equipment found in shops and factories to be mounted on isolation springs or mounts to dampen the transmission of machine vibrations to the floor. As equipment becomes heavier and more complex, the design of such isolators frequently fails to provide the intended isolation. Such isolators, sometimes referred to as base isolators, are usually designed to be placed in an environment wherein the principal vibrations emanating from a mounted machine or equipment group is within a known frequency range. The isolators are ideally designed having a natural frequency or period approximating the frequency of the machine vibration that the isolator is intended to dampen or isolate. The use of metal springs, for example, permits the design of an isolator having a predetermined fundamental frequency; however, that frequency is proportional to the square root of the mass of the machine that the isolator is to support. Therefore, if more than one isolator is to be used to support the machine (there are always several isolators) the isolators must be designed to provide the desired natural frequency while supporting a predetermined proportion of the machine mass. The mass of a machine or similar equipment is seldom configured or distributed in a manner that machine mounts can each carry the identical weight. Under such circumstances, machine base isolators of the prior art frequently encounter design requirements wherein the position of the isolator results in greater or less weight to be supported by the isolator than similar isolators being used at different positions on the same equipment. If the weight or mass supported by the isolator varies from the mass utilized in its design, the natural frequency of the isolator will be inappropriate for that machine base location. Further, the weight acting on a particular spring varies depending on the specific speed of the machine at any given time; that is, the static and dynamic center of gravity are not necessarily identical.
A machine base isolator that provides a predetermined natural frequency independent of the mass of the machine to be supported would permit such isolators to be utilized at convenient support locations for the machinery and equipment substantially without regard to the proportion of the total mass or weight of the equipment that the individual isolator is to support. The isolator would then function appropriately at the selected frequency or period essentially without regard to the mass that it is supporting.
Seismic disturbances can be particularly devastating to factories and shops having machines and equipment that are displaced during such seismic activity. Prior art machine based isolators designed to attenuate or dampen the transmission of vibration from a machine to a factory floor do not ordinarily provide seismic isolation. Violent seismic activity usually results in the destruction of the isolator mounting with the subsequent movement of the machinery along the factory floor. The crashing of a displaced machine into adjacent equipment or machines can be particularly devastating. To compensate for this deficiency, prior art techniques have included the utilization of bumpers or "snubbers"; that is, anchors having rubber coatings positioned at predetermined distances from machine bases to limit (but not prevent) the displacement of the machine in response to a seismic disturbance. The difficulty with the utilization of such snubber or bumper techniques is the fact that when the machine strikes the bumper, it has already been placed in motion and thus represents substantial kinetic energy which must be absorbed to bring the equipment or machine to rest. Energy absorption through the utilization of bumpers attempts to dissipate this kinetic energy in a very short distance which by its very nature creates tremendous forces. The force required to decelerate a massive machine that has been, or is being, displaced by seismic motion is usually beyond the strength of all but the most massive bumper systems.
A seismic isolation system would dissipate energy immediately upon lateral acceleration of the machine and would utilize friction induced heat and the energy required in bending mountings to absorb and dissipate energy to prevent movement of the machine beyond the limits of deformation of the machine base isolator.